1. Field of the Invention
The present invention relates to an optical disk, an optical disk recording and reproducing apparatus, a method for recording, reproducing and deleting data on an optical disk, and an information processing system. In particular, the present invention relates to an optical disk, an optical disk recording and reproducing apparatus, a method for recording, reproducing and deleting data on an optical disk, and an information processing system which can prevent unauthorized digital copying from being performed from an optical disk, on which data such as AV data (Audio and Visual Data) including image data of movies and audio data of music which are protected with copyrights is recorded, to another recording media such as an optical disk of another recording type or the like.
2. Description of the Related Art
An optical disk is superior in random accessibility to conventional tape media, and has such an advantage in that deterioration of the optical disk due to repetitive use is reduced because of being capable of non-contacting recording and reproducing by using a laser light. Further, the optical disk has such an advantage in that the optical disk can be mass produced at low cost by mastering performed by disk manufacturers, and a CD (Compact Disc) becomes generalized as a high quality digital audio instead of a conventional phonograph record for analog recording. Furthermore, a DVD (Digital Video Disk or Digital Versatile Disk) on which high quality image data has been digitally recorded has recently been commercialized, and the optical disk will be expected to be further developed as a digital recording medium for AV data in the near future.
On the other hand, in addition to a read-only optical disk on which data has been previously recorded in a pre-pit form by a disk manufacturer, such as a music CD, CD-ROM, DVD-ROM or the like, an optical disk of recording type (a recording type optical disk) on which a user can record AV data at home, such as CD-R, CD-RW, MO, MD, DVD-RAM or the like has been recently developed and has become widespread.
Also, in television broadcasts, digital systems for allowing multi-channeling or various services have been introduced instead of conventional analog systems, and such a trend will increase in the near future. In particular, the optical disk of recording type is expected to be utilized as recording media of content which is delivered through digitized broadcasting or communication for recording AV data which is mainly for the purpose of time shift utilization where, after contents are accumulated upon being delivered, a program selection is performed and the selected content is listened to or watched.
Conventionally, an optical disk of recording type which has been utilized mainly for computers is utilized for storing data which has been created by a user himself, and the optical disk of recording type does not have any means for preventing copying from being performed between two or more recording type optical disks. When the optical disk of recording type is widely utilized, an ordinary user copies recorded data of an optical disk to another optical disk of recording type irregularly as it is so that it becomes possible to obtain an unjust reproduction without paying the copyright royalty that is to be paid to an author or writer of the copied AV data and without any deterioration in the sound quality and image quality of the copied AV data because the optical disk of recording type is digitally recordable, which becomes a factor in preventing the spread of excellent content. Regarding an MD (Magentic Disk) on which music or the like is digitally recorded, means for performing generation management for limiting the number of recordings has been introduced where data, together with generation management data, is recorded on an optical disk and the number of permissible times the data can be copied is limited by the generation management data.
Also, in order to prevent the unjust copying of a CD-ROM or a DVD-ROM, for example, a method for forming a Burst Cutting Area (hereinafter referred to as a BCA), which is a write once area for overwriting a barcode on a pit section of an optical disk, and for recording respective disk IDs of each of the optical disks on the BCA which are different from each other and are assigned for each optical disk when the optical disks are manufactured has been proposed in an international application of International Publication No. WO 97/14144. According to this method, since a password is different for each disk ID, one password can decrypt only a cipher of one disk, and therefore, even when content is copied unjustly, the content cannot be decrypted due to the lack of information of a disk ID.
FIG. 39 is a block diagram showing a configuration of a user data area of a conventional DVD-ROM, and a configuration of an optical disk reproducing apparatus for decrypting an encrypted content from data in the user data area. In the DVD-ROM, as shown in FIG. 39, encryption is performed on content data that is recorded on a disk.
Referring to FIG. 39, the user data area of the DVD-ROM is constituted by a sector header area 3201, a main data area 3202, and an error detection code 3203. In this case, a sector address 3204 indicating a position of a sector, copyright control information 3205 on which the copyright control information regarding data that is recorded on the main data area 3202 (for example, a scramble flag, copy control information and the like) is recorded, and a decipher key 3206 for decrypting a cipher when the cipher is performed on data that is recorded on the main data area 3202 are each recorded on the sector header area 3201. Also, mainly AV data that are required for copyright protection and the like are encrypted and recorded on the main data area 3202.
At the time of reproducing such a user data area, a decipher key 3206 which is required for reproducing encrypted content from the sector header area 3201 is first acquired. The acquired decipher key 3206 is inputted to a key decrypting device 3207. The key decryption device 3207 decrypts the inputted decipher key 3206 into a content decipher key by using a predetermined disk key, and outputs the content decipher key to a decrypting device 3208. Next, the decrypting device 3208 decrypts the encrypted content of the main data area 3202 by using the decrypted content decipher key according to the copyright control information 3205 which has been stored on the sector header area 3201 corresponding to the main data area 3202, and then, the decrypted content which is reproducible data can be obtained.
In the optical disk according to the configuration shown in FIG. 39, it is possible to perform reading-out from the main data area 3202 through a driving apparatus of a personal computer or the like. However, an unjust reproduction or a production of a pirated version can be prevented by constituting the optical disk so that an area where the decipher key 3206 is recorded can be read out only by an optical disk reproducing apparatus with a regular authentication function.
However, for the unjust copying preventing method using the generation management data, the generation management data will be inevitably changed upon copying (i.e., changed from “once copying possible” to “copying impossible”). On the other hand, there is a problem in that unjust copying cannot be prevented sufficiently by copying data on the optical disk together with the generation management data without changing the generation management data or by altering the generation management data by a computer or the like and recording the data and the generation management data on the optical disk. Furthermore, since the number of permissible copies is limited based on the generation management data which has been previously recorded together with the content, there is a problem in that, even when a regular copyright royalty is paid, data which has been designated as “copying impossible” is not allowed to be copied to another optical disk at all, and a user must therefore wait for a content provider to provide the user with content data. Both of the above-described problems are caused because the content provider cannot manage content copying onto an optical disk of recording type performed by a user sufficiently.
Recently, personal computers are further improved in performance and they are also connected to networks so that cipher decryption can be performed at high speeds by a plurality of personal computers. In order to further increase the robustness of the cipher against such a decryption, it becomes necessary to extend a key length of a key which is used for the cipher. However, in a key management method for recording a decipher key in a sector header as is conventionally proposed, there is a problem in that only a decipher key with a size of a predetermined length (a size of decipher key area) or less is recorded, and a key length cannot be elongated for the purpose of improving the robustness of a cipher in the future.